Hepatitis C virus (HCV) is a (+)-sense single-stranded RNA virus that causes non-A, non-B hepatitis (NANBH). The virus is a small enveloped, single-stranded, positive sense RNA virus. It is the only known member of the hepacivirus genus in the family Flaviviridae. There are six major genotypes of the hepatitis C virus, which are indicated numerically as genotype 1, genotype 2, etc.
The natural course of chronic hepatitis C infection varies in different patients. Almost all patients show liver inflammation, but the rate of progression of liver scarring (fibrosis) varies significantly. It is estimated that about one third of untreated patients progress to liver cirrhosis in less than 20 years, and another third progress to cirrhosis within 30 years. The other third of patients progress very slowly and are unlikely to develop cirrhosis within their lifetimes.
The viral NS3 serine protease (NS3P) is responsible for proteolytic processing of the entire downstream region of the viral HC polyprotein, catalyzing cleavage at the NS3/NS4a, NS4a/NS4b, NS4b/NS5a, and NS5a/NS5b sites to release the mature NS3, NS4a, NS4b, NS5a, and NS5b proteins. The protease is therefore critical for viral replication and has been a target for drugs that inhibit protease function.